A GPRS is an approach to transmit data through a radio network, and has been developed with the concept of “packet switching” based upon a Global System for Mobile Communication (GSM) network. As illustrated in FIG. 1, a GPRS network 110 is a bearing network, specifically a two-layer bearing network, built on a GSM network, and is used to bear three-layer data packets, similar to an Ethernet network 120, a token ring network (not shown) and a frame relay network 130.
Based upon an existing GSM network, a GPRS network is accomplished with addition of some nodes in the existing GSM network. As an important network node in the GPRS network, a GPRS Supporting Node (GSN) is capable of mobile route management, and is adapted to connect various kinds of data networks, connect GPRS registers, transfer data and convert format between a mobile station and various data networks. The GSN may be a separate apparatus like a router, and may also be integrated with a Mobile Switching Center (MSC) in the GSM.
The GSN may be classified into two types: one is a Serving GSN (SGSN), and the other is a Gateway GSN (GGSN). The SGSN is primarily used to record current position information of a mobile station, and to transmit and receive mobile packet data between the mobile station and the GGSN. The GGSN primarily functions as a gateway, and may be connected with various data networks, such as Integrated Service Digital Network (ISDN), Packet Switched Public Data Network (PSPDN) and Local Area Network (LAN). The GGSN is also referred to as GPRS router in some literatures. The GGSN may perform protocol conversion for GPRS data packet in the GSM network so as to transmit the GPRS data packet to a remote Transfer Control Protocol/Internet Protocol (TCP/IP) network or X.25 network.
During operation, the GPRS network performs addressing and sets up a data connection by means of route management. However, this approach has some problems. For instance, when a dynamic IP address which has assigned to a mobile station previously is reassigned to another MS, a traffic initiated by the previous MS which used the address may be passed to the new MS which obtains the address, consequently, the new MS may have to pay for the extra traffic while no traffic has been applied on its own initiative. In particular, the process includes the following.
1. A mobile station MS 1 obtains an IP address, requests a network service, and then a GPRS Tunnel Protocol (GTP) tunnel is set up between the SGSN and the GGSN, and a session connection is set up between the MS1 and a WEB server.
2. When the WEB server starts transmitting a data packet to the MS1, if the MS1 sends to the SGSN a request for deleting the GTP tunnel and has not interrupted the session with the WEB server on its own initiative, the GGSN will discard the received data packet due to the absence of the GTP tunnel.
3. A new mobile station MS2 sends to the SGSN a request for setting up a GTP tunnel to the GGSN. The MS2 obtains the same IP address, and the SGSN sets up a new GTP tunnel to the GGSN. Because it is still receiving a data packet with the same destination address, the GGSN will forward the data packet to the MS2 upon detecting the new GTP tunnel for the destination address. As a result, the MS2 has to pay for a traffic which has not been requested.
In the prior art, a solution as illustrated in FIG. 2 is disclosed. An apparatus 230 is disposed between an SGSN 210 and a GGSN 220 to detect the status of a GTP tunnel, and another apparatus 250 is disposed between the GGSN 220 and a WEB server 240 to detect the session status of a connection between an MS 260 and the WEB server 240. The apparatus 230 and another apparatus 250 may communicate with each other based on a certain protocol. The apparatus 230 obtains a GTP tunnel, and if detecting that the GTP tunnel is deleted, notifies another apparatus 250 of the deleted tunnel as well as session information between the MS 260 and the WEB server 240. In accordance with the received information, another apparatus 250 deletes the session table for the MS 260 and the WEB server 240, and discards packets transmitted from the WEB server 240 to the MS 260.
However, this solution may have the following disadvantages.
1. The apparatus 230 is required to support the obtaining of the GTP tunnel protocol. The data stream between the GGSN and the WEB server includes normal IP packets, while the data stream between the SGSN and the GGSN includes packets of GTP tunnel protocol. If the apparatus is capable of obtaining the GTP tunnel protocol, it may detect the status of the GTP tunnel. The apparatus not only has to support each GTP protocol version, but also has to perform version updating when the SGSN and the GGSN update a GTP protocol version.
2. The networking mode has some limitations. Upon detecting that the GTP tunnel is deleted, the apparatus 230 sends a notification packet to the apparatus 250 only in two ways: the packet is sent from the apparatus 230 to the apparatus 250 directly; or the packet from the apparatus 230 is forwarded to the apparatus 250 via the GGSN. If both end addresses of the GTP tunnel set up by the SGSN and the GGSN belong to the same network segment, the operating mode of the apparatus 230 may only be a transparent bridge mode.
3. The failure rate of a single node is increased. There are a large number of traffics between the SGSN and the GGSN, and the apparatus 230 has to obtain packets of the GTP protocol package-by-package, which requires a powerful processing capability of the apparatus 230. In addition, the SGSN and the GGSN are located in a core position within the GPRS backbone network, and their stable operations are very important. However, the addition of the apparatus 230 may increase the possibility of node failure.
4. An operation cost is increased. Two apparatus provided in this solution are: the apparatus 230, which detects the status of the GTP tunnel, and sends to the apparatus 250 the tunnel deleting notification packet; another apparatus 250 which receives the notification packet, and deletes corresponding session. The two apparatus are indispensable.